1. Field of the Invention
The present invention relates to a calender having a frame and a roll stack, and more particularly to a calender having a lower deflection control roll device having a constant operational direction during adjustment.
2. Division of Background Information
A known calender is described in (German Patent Document No. DE 196 33 671 A1. This known calender is used for the treatment of paper and has a multiple roll stack having a vertical center plane. Bearing blocks for the lower roll (constructed as a deflection control roll) are held and guided on the frame in a linear guide. Beneath each of the bearing blocks, a loading device in the form of a hydraulic cylinder creates contact force exerted by the lower roll on the center rolls, which are mounted on levers above the lower roll. Contact force is also exerted on an immovably mounted upper roll. In this linear guide, frictional forces result which distort the loading forces and especially cause uneven loading at both roll edges.
Use of a pivoted arm substantially reduces the friction that results from movement of the bearing blocks of the lower roll. While use of this principle is known in conjunction with center rolls that are mounted on levers, when applying this principle to a lower roll that is constructed as a deflection control roll, the operating direction of the deflection control device (e.g. a series of hydrostatic support elements) changes. However, when the divergence of the operating direction of the center plane of the roll stack is more than about 1.degree. or 1.5.degree., additional sleeve stresses occur which can reach unacceptable levels and correspondingly result in damage. This problem is especially prevalent in areas where the lower roll does not always have the same operational position, because the diameters of the rolls in the stack change, or because only the bottom nip is supposed to be closed while all other nips are open. The lower roll must then be raised far less than when all nips are supposed to be closed.